CVE-2026-16221 (GCVE-0-2026-16221)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:08 – Updated: 2026-07-20 13:53
VLAI
Title
fast-uri vulnerable to host confusion via literal backslash authority delimiter
Summary
Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node's native WHATWG URL parser, used by fetch, undici, and Node's http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node's URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. Patches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3. Workarounds: none.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-436 - Interpretation Conflict
Assigner
References
Impacted products
Vendor Product Version
fast-uri fast-uri Affected: 2.3.1 , < 2.4.3 (semver)
Unaffected: 2.4.3 (semver)
Affected: 3.0.0 , < 3.1.4 (semver)
Unaffected: 3.1.4 (semver)
Affected: 4.0.0 , < 4.1.1 (semver)
Unaffected: 4.1.1 (semver)
Create a notification for this product.
Credits
rampage0010 mcollina UlisesGascon
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-16221",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-20T13:53:31.279563Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-20T13:53:42.583Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:npm/fast-uri",
          "product": "fast-uri",
          "vendor": "fast-uri",
          "versions": [
            {
              "lessThan": "2.4.3",
              "status": "affected",
              "version": "2.3.1",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "2.4.3",
              "versionType": "semver"
            },
            {
              "lessThan": "3.1.4",
              "status": "affected",
              "version": "3.0.0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "3.1.4",
              "versionType": "semver"
            },
            {
              "lessThan": "4.1.1",
              "status": "affected",
              "version": "4.0.0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "4.1.1",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "reporter",
          "value": "rampage0010"
        },
        {
          "lang": "en",
          "type": "remediation reviewer",
          "value": "mcollina"
        },
        {
          "lang": "en",
          "type": "remediation reviewer",
          "value": "UlisesGascon"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node\u0027s native WHATWG URL parser, used by fetch, undici, and Node\u0027s http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node\u0027s URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. \n\nPatches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3.\n\nWorkarounds: none."
            }
          ],
          "value": "Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node\u0027s native WHATWG URL parser, used by fetch, undici, and Node\u0027s http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node\u0027s URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. \n\nPatches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3.\n\nWorkarounds: none."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-436",
              "description": "CWE-436: Interpretation Conflict",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-19T14:08:32.993Z",
        "orgId": "ce714d77-add3-4f53-aff5-83d477b104bb",
        "shortName": "openjs"
      },
      "references": [
        {
          "url": "https://github.com/fastify/fast-uri/security/advisories/GHSA-v2hh-gcrm-f6hx"
        },
        {
          "url": "https://cna.openjsf.org/security-advisories.html"
        }
      ],
      "title": "fast-uri vulnerable to host confusion via literal backslash authority delimiter",
      "x_generator": {
        "engine": "cve-kit 1.0.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "ce714d77-add3-4f53-aff5-83d477b104bb",
    "assignerShortName": "openjs",
    "cveId": "CVE-2026-16221",
    "datePublished": "2026-07-19T14:08:32.993Z",
    "dateReserved": "2026-07-18T11:37:36.004Z",
    "dateUpdated": "2026-07-20T13:53:42.583Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-16221",
      "date": "2026-07-21",
      "epss": "0.00221",
      "percentile": "0.12729"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-16221\",\"sourceIdentifier\":\"ce714d77-add3-4f53-aff5-83d477b104bb\",\"published\":\"2026-07-19T15:16:49.027\",\"lastModified\":\"2026-07-20T15:16:36.150\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node\u0027s native WHATWG URL parser, used by fetch, undici, and Node\u0027s http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node\u0027s URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. \\n\\nPatches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3.\\n\\nWorkarounds: none.\"}],\"affected\":[{\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\",\"affectedData\":[{\"vendor\":\"fast-uri\",\"product\":\"fast-uri\",\"defaultStatus\":\"unaffected\",\"packageURL\":\"pkg:npm/fast-uri\",\"versions\":[{\"version\":\"2.3.1\",\"lessThan\":\"2.4.3\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"2.4.3\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"3.0.0\",\"lessThan\":\"3.1.4\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"3.1.4\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"4.0.0\",\"lessThan\":\"4.1.1\",\"versionType\":\"semver\",\"status\":\"affected\"},{\"version\":\"4.1.1\",\"versionType\":\"semver\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N\",\"baseScore\":7.5,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":3.9,\"impactScore\":3.6}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-07-20T13:53:31.279563Z\",\"id\":\"CVE-2026-16221\",\"options\":[{\"exploitation\":\"none\"},{\"automatable\":\"yes\"},{\"technicalImpact\":\"partial\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-436\"}]}],\"references\":[{\"url\":\"https://cna.openjsf.org/security-advisories.html\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"},{\"url\":\"https://github.com/fastify/fast-uri/security/advisories/GHSA-v2hh-gcrm-f6hx\",\"source\":\"ce714d77-add3-4f53-aff5-83d477b104bb\"}]}}",
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-16221\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-07-20T13:53:31.279563Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-07-20T13:53:37.076Z\"}}], \"cna\": {\"title\": \"fast-uri vulnerable to host confusion via literal backslash authority delimiter\", \"credits\": [{\"lang\": \"en\", \"type\": \"reporter\", \"value\": \"rampage0010\"}, {\"lang\": \"en\", \"type\": \"remediation reviewer\", \"value\": \"mcollina\"}, {\"lang\": \"en\", \"type\": \"remediation reviewer\", \"value\": \"UlisesGascon\"}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 7.5, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"vendor\": \"fast-uri\", \"product\": \"fast-uri\", \"versions\": [{\"status\": \"affected\", \"version\": \"2.3.1\", \"lessThan\": \"2.4.3\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"2.4.3\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"3.0.0\", \"lessThan\": \"3.1.4\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"3.1.4\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"4.0.0\", \"lessThan\": \"4.1.1\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"4.1.1\", \"versionType\": \"semver\"}], \"packageURL\": \"pkg:npm/fast-uri\", \"defaultStatus\": \"unaffected\"}], \"references\": [{\"url\": \"https://github.com/fastify/fast-uri/security/advisories/GHSA-v2hh-gcrm-f6hx\"}, {\"url\": \"https://cna.openjsf.org/security-advisories.html\"}], \"x_generator\": {\"engine\": \"cve-kit 1.0.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node\u0027s native WHATWG URL parser, used by fetch, undici, and Node\u0027s http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node\u0027s URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. \\n\\nPatches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3.\\n\\nWorkarounds: none.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node\u0027s native WHATWG URL parser, used by fetch, undici, and Node\u0027s http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node\u0027s URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. \\n\\nPatches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3.\\n\\nWorkarounds: none.\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-436\", \"description\": \"CWE-436: Interpretation Conflict\"}]}], \"providerMetadata\": {\"orgId\": \"ce714d77-add3-4f53-aff5-83d477b104bb\", \"shortName\": \"openjs\", \"dateUpdated\": \"2026-07-19T14:08:32.993Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-16221\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-20T13:53:42.583Z\", \"dateReserved\": \"2026-07-18T11:37:36.004Z\", \"assignerOrgId\": \"ce714d77-add3-4f53-aff5-83d477b104bb\", \"datePublished\": \"2026-07-19T14:08:32.993Z\", \"assignerShortName\": \"openjs\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.